The present invention relates to automotive emission storage canisters, more particularly, to an emission storage canister having a vent solenoid, and most particularly, to an emission storage canister having integral carbon absorber, vent solenoid, and high-efficiency air inlet vent filter.
Emission storage canisters are provided on automotive vehicles to prevent the discharge of fuel vapors outside vehicles during refueling, known as onboard refueling vapor recovery (ORVR), and also during extended periods of vehicle inactivity.
Typically, a canister containing activated carbon is mounted within a vehicle in communication, via a first or vapor inlet port, with the headspace in the fuel tank; via a second or vapor outlet port, with a vacuum source in the engine intake manifold; and via a third or vent port, with the atmosphere outside the vehicle. During refueling, the fill pipe is sealed against vapor leakage, either by a flexible gasket surrounding the fill nozzle or by a liquid seal in the fill pipe. As the tank is filled, air and vapors in the headspace above the fuel are forced through the vapor inlet port into the canister. The vapors are adsorbed onto the charcoal bed, and the air is discharged through the vent port. During subsequent operation of the vehicle, the engine vacuum draws air through the vent port, gradually purging the adsorbed vapors via the vapor outlet port into the engine""s combustion flow and preparing the canister for the next refueling. Air also flows back through the vent port into the fuel tank as needed to replace fuel being consumed by the engine.
The air vent port is normally open during periods of non-operation of the vehicle. Fuel tank vapors must be adsorbed by the canister before reaching the vent port. This function is known in the art as diurnal adsorption. Such diurnally adsorbed fuel is also desorbed and conveyed by vacuum to the engine upon startup.
Federal regulations require that each vehicle be equipped to conduct an onboard diagnostic (OBD) leak test of the evaporative emissions system. Several manufacturers use a vacuum decay OBD which requires apparatus for closing off the vapor outlet and vent ports, the vapor inlet port being effectively sealed during test by the fuel tank cap.
Typically, an ORVR canister is mounted immediately adjacent the fuel tank to minimize vapor flow restriction into the canister. Since the fuel tank commonly is located near the rear of the vehicle and the engine at the front, a relatively long hose run is required to connect the canister to the engine intake. A first electric solenoid valve at the canister can close the canister vent port, and a second solenoid valve at the engine can close the vapor outlet line. To test the system for leaks, first the vent port is closed, exposing the system to full engine vacuum, then the outlet line is closed. The OBD system monitors the rate of decay of the captured vacuum.
Mounting the canister at the rear of the vehicle exposes the vent port to dust and debris which, if allowed to enter the canister, can foul the vent solenoid and internal passages, gradually clogging the solenoid valve and the canister and causing failure of the seal test. Entry of dust and debris can also cause operational problems with refueling of the vehicle, including failure to fill properly and premature shutoffs of the refueling nozzle. To prevent such entry, a prior art approach, disclosed in U.S. Pat. No. 5,878,729 issued Mar. 9, 1999 to Covert et al. (""729) and incorporated herein by reference, provides two separate vent ports, an outlet vent port with a check valve for releasing fuel tank air during refueling, and an inlet vent port connected to the downstream side of the engine air filter. An additional check valve is disposed between the inlet vent port and the engine to prevent vapors flowing into the air cleaner during refueling and causing an over rich fuel/air mixture being fed to the engine at start up. This reference also discloses the concept of incorporating a filter directly into the canister housing ahead of the vent solenoid but rejects the idea as being xe2x80x9cof no real use for filtering the air vented to the outside during fuel adsorption, when it would merely serve as an air flow impediment.xe2x80x9d
A prior art canister, Model No. AK3612 manufactured by Knecht Filterwerke, GmbH, Stuttgart, Germany, incorporates a filter and vent solenoid in a refueling emission storage canister. This canister has several important shortcomings: a) the solenoid projects outwards from the canister, increasing significantly the space required for the canister; b) the flow path through the canister and solenoid requires a large, high-constant solenoid spring to open the vent valve because the vacuum force from the OBD system urges the valve toward the valve-closed position; c) a relief valve in the canister case prevents the engine vacuum from collapsing the fuel tank in the event the solenoid fails to open when OBD testing is completed; d) the filter media is flat, which minimizes the area available and thus the useful life of the media; and e) the filter media is permanently mounted and thus is not accessible for periodic cleaning or replacement as needed.
What is needed is an evaporative emission storage canister which integrates an inlet vent filter with a carbon adsorption bed and a vent solenoid in such a way that a) the filter does not serve as an impediment to reverse air flow through the filter, preferably over the expected lifetime of the vehicle in which the canister is mounted; b) the filter media is configured to maximize the filtration area consistent with the available volume of the filter box; c) the filter media is readily accessible for cleaning or replacement; d) the solenoid valve is disposed in a port within the body of the canister; and e) opening of the vent valve is assisted by OBD vacuum within the canister, and therefore a relief valve to protect the fuel tank is not required.
The present invention is directed to an improved onboard refueling vapor recovery canister for a vehicle including an unequally-divided carbon bed, a vent solenoid, and a high-capacity, self-cleaning vent filter. The integral configuration of the canister provides a significant reduction in the volume of space required to provide the recovery function and an increase in carbon volume over prior art canisters, permitting use of a lower grade carbon at a significant cost savings while meeting all working capacity requirements.
The canister is provided at an air inlet port with an internal filter box for a high-efficiency filter media, the filter box having a feature for receiving therein a canister vent solenoid for opening and closing on demand the air inlet port. The vent solenoid is retained in the filter box as by a twist lock or retaining clip.
Passages within the feature and the canister permit flow of air and/or fuel vapors through the filter, the solenoid valve, and the carbon bed. Preferably, the filter box is closed by a removable cover such that the filter may be removed for cleaning or replacement as needed.
In a preferred embodiment, the feature is semi-cylindrical with discontinuous radial ridges and the filter media is wrapped thereupon in a horseshoe-shaped configuration such that the filtration area is increased by more than 50% over that obtainable using a flat filter media within the same size filter box. The relatively large filtration area prevents outward air flow restriction during refueling. It was expected that such restriction might become significant with long use of the filter, but it has been found unexpectedly that the outward air flow serves to partially backflush the filter each time the vehicle is refueled, thereby extending the useful life of the filter media.
In a further preferred embodiment, the canister may be oriented such that particles flushed from the media surface which are not carried out of the canister can fall under gravity to the lower side of the filter box where they can accumulate harmlessly over a long period of canister use.
In a further preferred embodiment, the carbon absorber bed is divided into two sequential sub-beds of unequal length but equal cross-sectional area, the longer sub-bed being adjacent to the vapor inlet port. This configuration improves the diurnal efficiency (vehicle inoperative) performance of the canister relative to known canisters having equal length beds without increasing flow restriction of the carbon beds.